This proposal introduces a novel, non-invasive and painless method for the evaluation of skeletal muscle, using a recently developed technique called electrical impedance myography (EIM). The ultimate goal of this research is to refine ElM as a clinical test that can assist in the diagnosis and treatment of neuromuscular disease and in evaluation of muscle change due to disuse. In addition to complementing and potentially replacing the painful test of needle electromyography, ElM will have unique application in the evaluation of muscle weakness in clinical trials research, rehabilitation, and space flight. Our first aim is to establish normal values and confirm the reproducibility of this technique by performing studies on healthy subjects of varying age and fluid status. Second, patients with different disease and disuse states will be evaluated to determine ElM patterns associated with myopathy vs. neurogenic disease and compare the specificity and sensitivity of these patterns to well-established diagnostic methods. Finally, ElM's use as a tool in evaluating neuromuscular disease progression/remission will be assessed and refined. As part of this aim, a prototype device for easy use will be developed and tested in the clinical setting.